2790results about "Polyphase network asymmetry reduction" patented technology

A method and apparatus are described for controlling the flow of power in each input line to a three phase AC inductive load in order to reduce the amount of VAR in the system, and thus increase the operational efficiency of the inductive load. Solid state relays are positioned in series in each of the three inductive load line inputs, and current allowed to flow to the inductive load only during the time during which the SSRs are in a conducting state. The calculation of VAR is achieved by processing data from each of the input lines using a separate controller boards each dedicated to each of the lines. The controller in turn, based on the calculated VAR, increments the time, either increasing or decreasing it from a predetermined value, during which the SSRs in that line remains in the non-conducting state.

A method of converting a direct voltage generated by a decentralized power supply system into three-phase alternating voltage by means of a plurality of single-phase inverters (WR1-WR3), said alternating voltage being provided for supplying an electric mains, is intended to avoid inadmissible load unbalances using single-phase inverters. This is achieved in that, upon failure of one inverter (WR1-WR3), an asymmetrical power supply distribution is reduced by limiting the output of the other inverters. The method makes it possible to simplify three-phase voltage monitoring.

The invention relates to a method and device for performing on-load scheduling on a single-phase load in the intelligent power grid field. A master controller is mounted at an input end of a three-phase wire, a secondary controller is mounted at each single-phase branch of the wire, and the master controller exchanges information with the secondary controllers through communication interfaces. When the wire power unbalanced degree is over limit, the master controller optimizes and formulates a control scheme to operate the secondary controllers to convert the single-phase load between the phases; in the conversion process, the load is free from instant power off, and the power grid is free from impact and interference; and therefore, the distribution circuit dynamically runs in a load balance state, the unbalanced consumption problem of the circuit is completely solved.

The invention discloses a self-healing control method for operation of an urban distribution network, which is used in an operated urban distribution network. The method adopts an integrative coordination control mode of the urban distribution network based on the self-healing control technology; the process of signals and the generation of control strategies have self adaptability; the method automatically finishes a control process without external intervention, coordinates the action behaviors of a relay protection device, a switch, a safe automatic device and an automatic adjusting device, and carries out coordination control on the relay protection device, the switch, the safe automatic device and various automatic adjusting devices and parameters thereof so as to realize the technical proposal of stable, safe, reliable and economic operation of the urban distribution network; and the method belongs to the application field of cross technology of power system theory, control theory and artificial intelligence.

The invention discloses a control method for increasing asymmetrical fault ride-through capability of a wind power system. In the method, a super capacitance energy storage system is assessed between a machine side rectifier and a net side inverter on the basis of the prior art. On the control aspect, besides the control for the machine side rectifier and the net side inverter, the control for a super capacitance energy storage system is additionally provided in the method. Through controlling the coordination of the machine side rectifier and the net side inverter, a unit can realize the maximum wind energy tracking, grid-connected active and reactive power adjusting and grid-connected three-phase current symmetry and the stability of the voltage for a direct-current busbar between the machine side rectifier and the net side inverter when a power grid is normal is assured. The additionally provided super capacitance energy storage system is further controlled, the voltage stability of the direct-current busbar of the unit while the power grid has asymmetrical faults is assured, especially the grid-connected three-phase current symmetry is assured and the double power frequency ripple wave of the voltage of the direct-current busbar while the power grid has asymmetrical faults is removed so that the asymmetrical fault ride-through capability of the wind power system is enhanced.

The invention discloses a power compensation method for unbalanced direct power control of a voltage controlled grid-connected inverter, which is suitable for direct power control (the conventional direct power control) without synchronous speed rotational coordinate transformation. The method comprises the following steps of extracting negative sequence voltage signals and positive sequence current signals by collecting voltage and current signals of a three-phase electric network; and computing compensation items of active and reactive power according to selected control targets. In the method of the invention, the compensation items of active and reactive power are injected in the power reference signals of the conventional direct power control according to required control targets so as to respectively eliminate negative sequence current, double frequency fluctuation of the active power and double frequency fluctuation of the reactive power in the electric network, caused by unbalanced voltage in the electric network, and fit different application situations. The invention has the advantages of enhancing the capabilities of control and uninterrupted operation of the voltage controlled grid-connected inverter when the electric network is in an unbalanced fault.

The invention dsiclsoes a microgrid system with an asymmetric non-linear load and a power balancing control method. The system comprises a plurality of DG units connected in parallel and line impedors connected with all DG units. The line impedors are connected to a microgrid bus by PCC points. A three-phase balancing resistive load, an asymmetric linear load, and a diode rectifier non-linear load of a load unit are connected to the microgrid bus by PCC points. A measurement module for measuring voltage fundamental wave positive sequence and negative sequence components and harmonic wave components of the PCC points is also connected to the microgrid bus. The microgrid bus is connected with a 10-kV main power grid by a static switch and a transformer successively. According to the invention, reactive and harmonic power balancing of the microgrid is realized by using a selective virtual impedance based on the virtual fundamental positive and negative sequence impedance and the virtual variable harmonic impedance; a harmonic and unbalancing voltage compensation controller enables equal division of an unbalanced power and a harmonic power to be realized; and a problem of unbalancing of the harmonic wave and the voltage of the microgrid can be solved.

An uninterruptible power supply (UPS) system that includes a multiphase AC output configured to be coupled to a load, an inverter having an output coupled to the AC output and a control circuit operatively associated with the inverter and configured to cause the inverter to compensate for a phase imbalance of a load coupled to the AC output while power is being delivered to the load from an AC power source independently of the inverter.

A system, method and device for determining load profile of a power line conductor supplying power to a plurality of power customers is provided. In one embodiment the system comprises an automated meter reading system configured to receive meter data comprising data of the power consumed by each of the plurality of power customers as measured by the power meters; a phase detection system configured to determine one of the plurality of power lines to which each of the power meters is electrically connected; a meter grouping system configured to determine groups of power meter that are commonly connected to the plurality of power line conductors; and a load profile system configured to determine a load profile for each group of power meters by combining the meter data from each meter of each group over a plurality of time periods.

The invention relates to an electric locomotive non-power-off neutral section passing-electric energy quality comprehensive compensation device and method, which belongs to the technical field of railway transport equipment and electric electronics. The device comprises a controllable transfer switch, a single-phase step down transformer, a single-phase step down transformer with a middle tap, a two-phase back-to-back converter sharing a DC-side capacitor, a circuit breaker switch, four position sensors and three electric quantity sensors. In the method, when the electric locomotive passes the neutral section, the controllable transfer switch is turned off, and the device works in a non-power-off neutral section passing mode to perform control on amplitude and phase of the neutral section voltage and enable the electric locomotive to pass the neutral section with load in a non-power-off manner. Without locomotive passing, the controllable transfer switch is closed, and the device works in an electric energy quality comprehensive compensation mode and has functions of active power transfer as well as inactive power and harmonic compensation. Through the device, the problems relating to electric energy quality of a traction substation and neutral section can be comprehensively solved based on the traditional traction power supply mode.

An apparatus for providing phase rotation for a three-phase AC circuit. The apparatus comprises three phase input terminals and three phase output terminals, where a first phase input terminal is coupled with a third phase output terminal; a second phase input terminal is coupled with a first phase output terminal; and a third phase input terminal is coupled with a second phase output terminal.

The invention discloses a distributed type power supply zone branch circuit three-phase load current balance monitoring method and device and belongs to the field of power supply and distribution devices. At least one three-phase load current balance main controller is arranged, load current signals of each phase circuit in each branch loop are collected, according to the obtained load current signals of each phase circuit, the three-phase current unbalance rate or the mean value of the three-phase current unbalance rate of each branch loop is computed, and the unbalance situation of three-phase load current of each branch loop is judged. The magnitude of load current in each unit meter box of each branch loop is collected, and the phase of unit meter box load which needs to be adjusted is determined. According to the three-phase load current unbalance situation of a certain branch, a control instruction is issued to an automatic phase-changing switch in a unit meter box corresponding to the branch loop, converting of load phases is carried out, adjusting of three-phase load current balance of each branch loop on the low-voltage side of a distribution transformer is achieved, and the real balance of distribution transformer low-voltage side main loop three-phase load current is guaranteed.

The invention relates to a method for controlling a wind park comprising several wind power installations to feed electrical power into an electrical AC grid at a point of common coupling (PCC). The method comprises feeding a 3-phase current at a point of common coupling, identifying a grid voltage on the point of common coupling, comparing the grid voltage that was identified on point of common coupling with at least one predetermined set point value, determining set point values for wind power installations depending on a comparison conducted to meet a stability criterion on point of common coupling, passing the determined set point values to plant control units of the individual wind power installations, and producing electrical current at each of the wind power installations depending on the predetermined set point values to be jointly fed in on point of common coupling.

The invention discloses a power quality comprehensive compensation system of an electric railway and a control method thereof. The system comprises a railway static power controller RPC and two sets of thyristor switched capacitors TSC. The thyristor switched capacitors bear a large proportion of reactive power compensation, RPC performs active power compensation, harmonic suppression and a remained small proportion of reactive power compensation for two power supply arms, therefore, the capacity of RPC is effectively reduced, and negative sequence, harmonic and reactive comprehensive compensation are realized. The control method comprises a cooperative control policy of RPC and TSC, reference current detection based on reactive separation, a reactive power distribution method and an RPC control method. The power quality comprehensive compensation system of the electric railway greatly improves the power quality of the electric railway with low cost, and the corresponding control method effectively coordinates the operation of RPC and TSC and ensures that the system has good compensation performance and favorable application prospect.

The invention provides an on-line three-phase load unbalance processing method suitable for a low-voltage distribution network. The on-line three-phase load unbalance processing method comprises the following steps of: monitoring three-phase load by three-phase load monitoring units on the low voltage side of a distribution transformer, and transmitting monitoring data to three-phase load unbalance monitoring units of the distribution transformer; judging whether the three-phase load unbalance exceeds a standard value or not by the three-phase load unbalance monitoring units of the distribution transformer; if the three-phase load unbalance exceeds the standard value, transmitting signals to an on-line load phase modulation control unit by a communication unit; judging whether the three-phase load unbalance of the distribution transformer is caused by the three-phase load unbalance of a main low-voltage circuit or not by the on-line load phase modulation control unit; and if so, setting an on-line load phase modulation strategy according to the monitoring data of the load monitoring units of branches of three phases of the main low-voltage circuit, sending a control command to an on-line load phase modulation switch combination unit by an on-line load phase modulation judging and controlling unit, and switching the load phases of the branches of users so as to realize the on-line three-phase load unbalance processing.

The invention discloses a low-voltage power grid three-phase imbalance adjustment method based on a phase-change switch. A difference between average current and the inter-phase maximum current is calculated, an average current fixed value and an inter-phase maximum current fixed value for starting imbalance adjustment is calculated according to transformer capacity and a load rate, three-phase transfer load is calculated, a load transfer direction is determined, the phase actually needs to transfer load out if the load which needs to be transferred is positive, the phase actually needs to receive load if the load which needs to be transferred is negative or zero, a phase-change switch which needs load transfer and a transferred target phase are determined according to the phase and the actual load of each phase-change switch, a phase-change switch action queue is generated, the phase-change switches are sequentially controlled to perform load transfer until all phase-change switches complete load transfer, and the system thus achieves the best balance state in the current condition. The method is used for low-voltage power grid three-phase imbalance treatment, the three-phase imbalance degree is reduced, voltage drop is reduced, power supply voltage treatment is improved, and line loss is reduced.

Disclosed are an automatic three-phase unbalanced load compensation experimental device and its control method. The experimental device comprises an automatic compensation device, a load simulation part, and detection, display and control parts. The automatic compensation device comprises power capacitors and intelligent grouping compound switches; the detection, display and control part comprises current transformers, molded case circuit breakers, a three-phase digital display ammeter, a three-phase electric power monitoring instrument, a protocol conversion module, 485 buses, Ethernet cables and an upper computer; the load simulation part comprises phase A, B and C loads which are in star connection and are same in component and circuit connection, an analog output module and a relay output module. Power monitoring instrument and digital ammeter are connected to the grid by circuit breaker and current transformer. The automatic compensation device and load simulation part are connected to the grid in parallel.

Described herein are embodiments of methods, devices and systems of phase identification for a meter. One aspect comprises a method of phase identification for a smart meter. One embodiment of the method comprises connecting a device to at least a first phase of a poly-phase electrical system; metering at least the first phase of the poly-phase electrical system that the device is connected to for electrical consumption information using a meter; storing a first phase identifier for the first phase of the poly-phase electrical system that the device is connected to in a memory associated with the meter; and transmitting at least the first phase identifier over a network operably connected with the meter.

The invention discloses a single-phase combined in-phase power supply and transformation structure mainly comprising a traction transformer and a CPD. In the CPD, a high-voltage matching transformer primary side and a traction transformer primary side form an SCOTT connected group, a secondary side winding of the CPD is connected to the incoming end of an AC-DC-AC converter, and the outgoing end of the AC-DC-AC converter is connected with the primary side of a traction matching transformer. A secondary side winding of the traction transformer and the secondary side winding of the traction matching transformer are equal in voltage amplitude and phase and both connected with a traction busbar; traction load calculated capacity is equal to the sum of traction transformer calculated capacity and CPD calculated capacity, the traction transformer is responsible for main power supply, and the CPD calculated capacity is determined by the capacity of traction load which caused exceeding three-phase voltage unbalance. The single-phase combined in-phase power supply and transformation structure has the advantages that optima configuration of traction power supply resources is realized and energy conservation is better.

The invention relates to an electric energy adjustment device for active and reactive power adjustment of a high-voltage system, which belongs to the field of electric and electronic technology. The device realizes high-voltage synchronization by adopting a mode of cascading a plurality of shingle-phase full-bridge inversion units, adjusts reactive power and instantaneous active power output by the device, or compensates for phenomena, such as low voltage and three-phase unbalance at a synchronization position, by controlling the charge and discharge of a big capacitor on the direct-current bus of each inversion unit, and adjusts the stable active power output or stored by the device by using an assembled battery unit on the direct-current bus of each inversion unit. The adjustment device of the invention integrates functions of active power adjustment and reactive power adjustment, has strong dynamic adjustment capability, needs no transformers, occupies a small area, has no harmonic wave of output, is simple in maintenance and has relatively comprehensive functions and outstanding cost performance.

A method of converting a direct voltage generated by a decentralized power supply system into three-phase alternating voltage by means of a plurality of single-phase inverters (WR1-WR3), said alternating voltage being provided for supplying an electric mains, is intended to avoid inadmissible load unbalances using single-phase inverters. This is achieved in that, upon failure of one inverter (WR1-WR3), an asymmetrical power supply distribution is reduced by limiting the output of the other inverters. The method makes it possible to simplify three-phase voltage monitoring.

A reactive power compensation device based on novel modular multilevel topology and a control method thereof relate to a high-voltage and large-power reactive power compensation device. In the prior art, compensation in a high-voltage and large-power field is limited and an inhibiting ability to circulation is insufficient. The invention aims at solving the above problems. A three-phase alternating-current power supply, a resistance-inductance load, a MMC converter, a signal detection circuit, a control circuit and a driving circuit are included. The MMC converter comprises three bridge arms which share a same structure and are connected in parallel. Each bridge arm comprises an upper bridge arm and a lower bridge arm which are symmetrical about a middle point of the bridge arm and are connected in series. Each upper bridge arm comprises a resistor, an inductor, several half-bridge units and an H bridge unit which are connected in series. The inductor of each upper bridge arm and an inductor of each lower bridge arm are connected in series. The middle points of the three bridge arms of the converter are connected in parallel between the three-phase alternating-current power supply and the load through a lead. By using the device and the method in the invention, power-grid reactive power can be compensated; a three-phase imbalance problem of a system is solved; effects of supporting a power grid voltage and inhibiting the circulation are achieved.

The invention discloses a single-phase and three-phase combined in-phase power supply and transformation device which comprises a single-phase traction transformer, a three-phase YNd11 grounding compensation transformer and a single-phase in-phase compensation device thereof; the in-phase compensation device comprises an alternating current-direct current-alternating current (AC-DC-AC) converter; the traction transformer and the compensation transformer have equal effect to a three-phase and two-phase balance transformer with the phase of secondary side voltage being vertical; when in a normal state, the traction transformer, the compensation transformer and the in-phase compensation device jointly supply power for a transaction load by a specified proportion; when the compensation transformer or the in-phase compensation device exit the operation, the traction transformer can work independently in a short time; and a backup traction transformer can replace the traction transformer to work and can work on linear voltage different from that of the traction transformer. According to the device, the electric phase at the exit of a traction transformer substation can be canceled, so that the electric energy quality requirements mainly comprising the unbalance of three-phase voltage can be met, and the optimal configuration of traction power supply resources can be realized.

The invention provides a three-phase imbalance three-phase imbalance method for a power distribution network with distributed power supplies. The three-phase imbalance three-phase imbalance method for the power distribution network with distributed power supplies comprises: aiming at the complex power distribution network, on basis of the fundamental principle of the implicit Gaussian load flow calculation method.

The invention discloses a microgrid control method having functions of voltage unbalance compensation and harmonic suppression. An integrated controller acquires a common bus voltage and calculates an unbalance factor vector, a characteristic order harmonic component positive-sequence compensation reference vector and a characteristic order harmonic component negative-sequence compensation reference vector of the common bus voltage, and transmits the vectors to a local controller of every parallel inverter through low-bandwidth communication. In the local controller, a characteristic order harmonic positive- and negative-sequence compensation voltage vector is calculated and is superposed with a reference voltage vector, a virtual impedance voltage vector and the common bus voltage unbalance factor vector to synthesize and correct a voltage regulating reference vector, and unbalance compensation and harmonic suppression of the common bus voltage is carried out through inverter voltage and current control. By applying the method provided by the invention to a multi-inverter parallel system in which a common bus is connected with a three-phase unbalanced load and a nonlinear load, three-phase voltage balance of the microgrid can be maintained, output voltage distortion of three-phase inverters can be reduced, and output power of the parallel inverters can be accurately allocated.

A system is provided for mitigating an electric unbalance of a three-phase current at a Point of Common Coupling being located between a wind farm having a plurality of wind turbines and a power grid. The system includes a measurement device and a central wind farm controller. The measurement device measures the electric unbalance at the Point of Common Coupling and provides a measurement signal being indicative for the measured electric unbalance. The central wind farm controller is coupled to the measurement device and controls the operation of the plurality of wind turbines. In response to the measurement signal the central wind farm provides a control signal for mitigating the electric unbalance at the Point of Common Coupling. Also provided is a corresponding method for mitigating an electric unbalance of a three-phase current and a computer program for controlling and / or for carrying out the mentioned method.

Disclosed is an intelligent low-voltage power load distribution system and method. The system comprises an intelligent low-voltage power load distribution host and a plurality of intelligent power load distribution terminals. The intelligent low-voltage power load distribution host comprises a current transformer, a voltage transformer, a CPU (U6), a liquid crystal display and a three-phase communication module. One intelligent power load distribution terminal comprises a large current transformer, a voltage transformer, a high-power magnetic latching relay, a high current composite switch, a three-phase switch interlock circuit, a communication module, a phase identification circuit and a CPU (U12). According to the intelligent low-voltage power load distribution system, the distribution transformer and the load distribution terminals are provided with an intelligent low-voltage power load distribution host and intelligent low-voltage power load distribution extensions, the intelligent low-voltage power load distribution method is adopted, automatic phase switching is performed on parts of unbalanced loads, and normal operation of distribution transformer low-voltage electric load is guaranteed; the system and the method are adaptable to intelligent distribution transformer power load distribution of a power system.

In a multiphase electrical power construction and assignment, a processor: determines a phase and voltage configuration for bi-directional power device pairs; determines a given bi-directional power device pair is to be coupled to a given phase connection based on the configuration; determines whether the given bi-directional power devices in the given bi-directional power device pair are to be coupled to each other; confirms that the given bi-directional power device pair is not coupled to any of the plurality of phase connections; couples the given bi-directional power device pair to the given phase connections, where power signals of the given bi-directional power device pair are synchronized with a power signal of the given phase connection; and in response to determining that the given bi-directional power devices are to be coupled to each other, couples each of the bi-directional power devices to a short bus.

Three phase power flow analysis of an unbalanced power distribution system decouples voltage changes resulting from nodal admittance matrix into one contribution from a real part, conductance matrix, and other contribution from an imaginary part, and a susceptance matrix. A first voltage change and second voltage change resulting from conductance and susceptance matrices are determined respectively. The voltages of a node of the power distribution system are determined as a combination of first and second voltages.

The invention discloses a STATCOM unbalance compensation control method based on a modular multilevel converter (MMC). The method comprises a converter compensation current dead-beat control method and a converter interphase circular current active damping control method. A comprehensive compensation current dead-beat control part is used for compensating active loss in the MMC by controlling active current, reactive current and negative-sequence current which are output by the MMC so as to eliminate unbalance of the current of a power grid and compensate reactive power; the interphase circular current active damping control method is used for summing by detecting the bridge arm current of upper and lower bridge arms of each phase and multiplying by 0.5 to obtain the circular current of each phase, and superposing the output of three-phase current passing through an active damping controller to dead-beat control output so as to inhibit the alternating current component of the circular current, reduce the current stress of converter devices and reduce the loss of the converter. Through the adoption of the method provided by the invention, compensation of the negative-sequence current and reactive current of unbalanced load of the power grid is realized, inhibition of the interphase double frequency circular current of the MMC is simple, the response speed is high and the stability is high.